In television broadcast systems compliant with DVB standards, related video, audio and data content, such as video audio and program guide data for a single TV channel or group of TV channels, is processed by a broadcaster head-end system for delivery to receivers in an MPEG-2 data stream called a transport stream (TS). A transport stream comprises one or more content streams referred to as packetized elementary streams, each packetized elementary stream (PES) typically containing the data for one video, audio or data content aspect of one of the television channels. Each packet of a PES is typically spread across many smaller transport stream packets for broadcast, with the transport stream packets for the multiple PESs being multiplexed into a single transport stream for transmission.
Provisioning of protected DVB services is typically enabled using a conditional access (CA) system. Content data is encrypted in a broadcaster head-end system and delivered to receivers in TS packets along with metadata enabling each receiver to use the correct key, commonly referred to as a control word, to decrypt the content. Control word provisioning may be achieved using a smartcard, or other conditional access/digital rights management (CA/DRM) client at the receiver. Control words are usually sent to the receivers in encrypted form within entitlement control messages (ECMs) delivered in the TS using MPEG-2 sections alongside the PESs carrying video, audio and/or other data. The CA/DRM client decrypts data in the ECMs to retrieve the control words, using product keys which are updated periodically using entitlement management messages (EMMs), and delivers the control words as required to one or more decrypters in the receiver.
Digital watermarking of content is well known. The content may comprise any type of information, and may include one or more of audio data, image data, video data, textual data, multimedia data, a web page, software products, security keys, experimental data or any other kind of data. There are many methods for performing digital watermarking of content but, in general, they all involve adding a watermark to an item of content. This involves embedding, or adding, watermark symbols (or a watermark codeword or payload data) into the original item of content to form a watermarked item of content. The watermarked item of content can then be distributed to one or more receivers (or users or recipients or receivers).
One particular application of digital watermarking is in the delivery of video signals in a digital video broadcasting (DVB) system, although many others exist.
WO01/67667 describes a technique in which content can be delivered in a encrypted form to a plurality of receivers in such a manner that the content stream recovered at each receiver or subset of receivers carries a different set of watermark symbols, or fingerprint, from that recovered at other receivers or subsets of receivers. This is achieved by including in a content stream multiple (typically two) copies of some or all portions of the content, each copy carrying a different watermark symbol and being encrypted using a different control word than the other copies of the same content portion. By controlling the control words available at each receiver, the set of watermark symbols, or fingerprint, present in a content stream reconstructed at each receiver is controlled.
EP2341708 describes a similar scheme in which error handling capabilities of the receivers are used to reject content portions which are decrypted with the wrong control word, so that only the intended watermark symbols are found in the reconstructed stream at a particular receiver.
EP2334070 describes ways in which the broadcaster head-end may be arranged to generate a suitable encrypted content stream for delivery to receivers in order to implement a similar fingerprinting scheme.
It would be desirable to be able to implement a scheme for delivering content multiple, differently processed copies of at least selected portions of content in a single transport stream to a plurality of receivers by adding extra functional modules to a conventional head-end system and avoiding or minimising reengineering of existing functional modules, so that such a scheme can be more easily integrated into an existing or already designed broadcaster head-end system. The invention seeks to address this and other problems of the related prior art.